This invention relates to a method of operating a heat pump system in an absorption heat pump mode and/or boiler heating mode, wherein a solution of a refigerant in a solvent is heated in a boiler, the resultant evaporated refrigerant is delivered to an absorber through a condenser, a throttle and an evaporator when in the heat pump mode, or directly to the absorber when operating in the boiler heating mode, and wherein the refrigerant is combined with the solvent that is drawn, low in refrigerant, from the boiler and the resulting rich solution is returned to the boiler, the system being of the type allowing for its shut down by turning off the heating of the boiler.
The invention also relates to a heat pump system comprising a heated boiler, a refrigerant conduit leading from the boiler through a condenser, a throttle and an evaporator, to an absorber, further a conduit through which the solvent, low in refrigerant, is passed to the absorber, and a return conduit leading from the absorber to the boiler. The heat pump system to which the invention pertains is especially adapted to operate in accordance with the method of the present invention.
In known absorption heat pump systems, the boiler is heated by means of a gas or oil burner unit or by an electrical heater whereby refrigerant vapor is expelled from the solvent containing the refrigerant. Both pressure and temperature of the vapor are consequently elevated to a high level respectively. The vapor passes from the boiler to a condenser where it gives up the heat of condensation and condenses.
Ambient energy can be transferred in the evaporator to the highly cooled expanded refrigerant.
The refrigerant flowing from the evaporator is absorbed in an absorber into the solvent, low in refrigerant, that is drawn from the boiler. The resulting heat of solution and heat of mixing are carried off to a receiver. The enriched solution produced is pumped from the low pressure level of the absorber, (approximately evaporator pressure) to the high pressure level in the boiler.
Should the heating of the boiler be turned off, further amounts of refrigerant vapor will be expelled for some time due to the thermal capacity of the boiler until, first, the pressure equalizes between the low-pressure area and the high-pressure area, and secondly, the boiler temperature drops below the boiling point. In the meantime, the stratified concentration in the boiler is reduced and brought down to the lean solution level. In order to bring the process back into operation, the boiler temperature must be elevated by the heating energy, first to the boiling state and then to the level corresponding to the high pressure required. During that intermittent starting procedure, the concentration stratification necessary for a steady working condition in the boiler can only be restored through a progressive supply of the rich solution. Start-up time of considerable length, and energy losses must also be tolerated when such a system is to be returned to operation.